I have mocked up the 915 with a spare T4 case, crank and 228mm wbx flywheel. The measurements from the edge of the bellhousing on the 915 to the ring gear of the 228mm FW are identical to the same setup on my 901 gearbox ! The 228mm PP fits with no clearancing issues either.
I am thinking I can just use the stock 901/914 starter and all will be well. I will hook up the starter tonight with a battery and see if it engages like I think it will.
The only issue remaining then would be the clutch engagement, I think easily fixed by using the BAFS TOB sleeve and T3 TOB for a push clutch and then a hydraulic slave to actuate.
Seems simple
Sandeep